The current trend is to supply products, especially ophthalmic products, that do not contain preservatives. The sterility of the product must thus be guaranteed throughout the use of the bottle containing the liquid to be delivered.
From document WO92/01625, various devices are known that enable the delivery of drops of product contained in a reservoir and which prevent contamination of the liquid remaining in the bottle.
According to one example, such a liquid dispensing device includes a reservoir and a dispensing tip mounted on the reservoir, provided with a liquid dispensing opening. The dispensing tip comprises a valve which allows liquid to exit but prevents it from entering, which limits the risk of introducing bacteria or contaminating substances into the bottle. Such a valve is also referred to as a “check valve”. The user applies pressure to the reservoir causing it to become deformed and, under the effect of pressure, a drop passes through the valve and forms on the surface of the dispensing opening. The valve closes once the desired quantity of drops is delivered.
A problem with this type of device is that although the valve closes, a small residual quantity of product remains on the surface of the tip after the dosed drop or drops are delivered and this small residual quantity of product may be the point from which contamination may spread into the bottle.
This propagation is a surprising phenomena which contradicts the operating principle of the valve, but which the inventors behind this invention have highlighted.
A posteriori, the inventors explain this phenomenon by the fact that the position of the boundary between the inside and the outside of the bottle is not fixed on the valve, but moves, over the course of successive openings and closings, around an average position. As a result, in the areas surrounding this boundary, there are adjacent areas that are sometimes inside or outside the bottle, i.e. outside the boundary, and sometimes included within this boundary.
After several opening-closing manoeuvres, the contaminations can find a path of slow migration via these adjacent zones, first from the outside of the bottle toward the boundary, then from the boundary toward the inside of the bottle.